Can you answer some questions so that I can understand what happening?

1. Do you have both the Arc and Arc Ultra setup in your home?
2. Were the surrounds were paired with the Arc before you got the Ultra?
3. Did you REMOVE the surrounds from the Arc BEFORE you set up the Ultra?
4. Is the Ultra replacing the Arc or are you placing it in another room?

Have you tried powering off the Arc while you setup the Ultra? 

Have you tried Basic Trurplay to tune the Ultra instead of Advanced Trueplay? Users have found the advances lowers the volume for the Sub and surrounds.

 Is the issue the same if the source is Dolby Atmos?

Hi Pools! Thanks so much for the reply.

1. The original arc in the main set-up has been relocated to a different part of the house. 
2. The surrounds were paired with the Arc before the ultra. 
3. The surrounds were removed from the Arc before the ultra
4. It is replacing the Arc in the main room

The Arc was powered off and unplugged and moved before the ultra was set-up.

I haven’t tried basic but I can. 

When I run surround test, the bass and surrounds play through the Ultra simultaneously. Can’t get it not to. Unless that’s part of the Atmos experience, but that wouldn’t make sense. 

In addition, the Ultra had to be hardwired into the amp, otherwise the surrounds and sub wouldn’t connect. (it would go through the entire set-up successfully, but then wouldn’t actually be attached). And then the amp is connected to my switch that controls the rest of the house.

The Magnolia installers think it may be something with the network and what was previously installed is still influencing the new hardware. The new didn’t just replace the old information. Not sure how accurate that is. 

Thanks for your time!

 What source are you using to test the surround speakers?  Is it a 5.1 test track that sends a tone to one speaker at a time?  What do you mean “hardwired into the amp”?

Is the Amp hardwired to your router? If so you may want to hardwire the Ultra instead and allow the Amp to pair ti it through its 5Ghz WIFI used to bond surrounds and a Sub. Ideally, you want to have a main speaker (soundbar or Amp) hardwired before you hardwire a Sub or surrounds.

What type of network do you have? 

The Amp is hardwired to the switch and that’s plugged into the router. 

Hardwiring the Ultra makes sense and then pairing amp and sub. I’ll play with that. Stay tuned!!!

Its the same issues over here now 2 pages long without an agreed solution.

Its not about Trueplay, not about how its connected. Not about Atmos or not Atmos….. seems to be a bug :(
 

Wait... I bet it will work just fine when they release the ERA 100 “Ultra” surrounds….

 In that linked topic someone stated with Dolby Atmos the test sound for the rear speakers was NOT duplicated in the Arc Ultra.  Only with 5.1 non Atmos was this duplication of the rear channel test sound also playing in the Arc Ultra.  
 
 There are some Atmos test files available to test channel ID in both Apple Music & Amazon Music Unlimited.  Just search for Dolby Labs.  I just wanted to know if the surround bug was also noted when the source is Dolby Atmos.  I don’t have the Arc Ultra yet to test this.

Hello, I tested with Tidal with Atmmos with Dolby Labs Tracks “functional testing”
Same issue :(

​@Ethancreativela 

Just FYI…

Sonos prefers a direct connection to a router versus going through a switch which can be problematic. That’s especially so if it’s a “managed” switch. However, Sonos has been know to function through an “unmanaged” (dumb) switch.